A method is generally known wherein a mixture of unsaturated hydrocarbons having 4 or more carbon atoms containing highly unsaturated hydrocarbons is reacted with hydrogen in the presence of a hydrogenation catalyst to selectively hydrogenate the highly unsaturated hydrocarbons into corresponding hydrocarbons of low unsaturation degree. For example, a method of selectively hydrogenating dienes and acetylenes only by reacting a mixture of unsaturated hydrocarbons having 4 carbon atoms containing the dienes such as butadiene, methylallene, etc.; acetylenes such as dimethylacetylene, ethylacetylene, vinylacetylene, etc.; and monoolefins such as 1-butene, 2-butene, isobutene, etc., with hydrogen in the presence of a hydrogenation catalyst such as palladium, platinum, nickel, etc., has been industrially employed.
However, in such a known selective hydrogenation method, there is a demerit that intramolecular transfer of double bonds easily occurs simultaneously with the selective hydrogenation to highly unsaturated bonds such as two or more double bonds and one or more triple bonds, whereby the composition of reaction product is greatly changed. For example, when a selective hydrogenation reaction of unsaturated hydrocarbons having 4 carbon atoms containing, for example, butadienes and butynes is performed, isomerization of 1-butene into 2-butene easily occurs simultaneously with the selective hydrogenation of butadienes and butynes into butenes, whereby the concentration of 1-butene in the reaction product is greatly reduced.
1-Butene is important as a monomer for producing polyolefins. Hence, from the viewpoint of effective utilization of 1-butene in a mixture of hydrocarbons having 4 carbon atoms, the development of a method capable of selectively hydrogenating highly unsaturated hydrocarbons only without being accompanied by isomerization has been strongly demanded.